Load sharing architecture for redundant channel controllers

ABSTRACT

A redundant, multi-source architecture provides output loads access to each of the plurality of power sources. The architecture includes at a least a first power bus and a second power bus. A plurality of loads are connected to the first power bus and the second power bus. Redundant first and second channel controllers are connected to receive power from the first power bus and the second power bus, respectively, wherein one of the first and second channel controllers is designated as the active channel controller. The active channel controller allocates power from both the first power bus and the second power bus to each of the plurality of loads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 12/777,002, entitled “LOAD SHARING ARCHITECTURE FOR REDUNDANT CHANNEL CONTROLLERS,” filed May 10, 2010 by Lillis et al.

BACKGROUND

The present invention relates to a power distribution system, and in particular to a redundant power distribution system.

Typically vehicles, such as an aircraft, utilize a power distribution assembly (PDA) to distribute power to various aircraft systems. Traditionally, a PDA includes an active channel controller associated with a first power bus and a standby or back-up channel controller with a second power bus. A single arbitration card provides a communication interface for both the active and back-up channel controllers. A common data bus is connected to each of the power modules and interfaces with the arbitration card. When healthy, the active channel controller provides power from the first power bus to the plurality of power modules or loads, while the back-up channel controller remains in a stand-by mode, providing no power from the second power bus to the loads. In the event the first channel controller fails, or the first power bus becomes unhealthy, the arbitration card switches control from the active channel controller to the back-up channel controller, which distributes power from the second power bus to the plurality of loads.

In this way, the traditional redundant architecture provides the requisite reliability for critical systems. However, this architecture requires that each power bus be capable of handling loading requirements for all attached loads. As such, circuit breakers or other protective devices associated with both the first and second power buses must be sized to handle the full loading requirements of each of the plurality of loads. The combined power rating of the circuit breakers is therefore underutilized during normal operation in which both or all power buses are healthy.

SUMMARY

A redundant, load-sharing architecture provides output loads access to each of the plurality of power buses. The architecture includes at a least a first power bus and a second power bus. A plurality of loads is each connected to the first power bus and the second power bus. Redundant first and second channel controllers are connected to receive power from the first power bus and the second power bus, respectively, wherein one of the first and second channel controllers is designated as the active channel controller. The active channel controller allocates power from both the first power bus and the second power bus to each of the plurality of loads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a redundant, load-sharing system according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a redundant, load-sharing system according to another embodiment of the present invention.

FIG. 3 is a flowchart illustrating steps performed by a channel controller employed in a redundant, load-sharing system according to an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides a redundant, load-sharing architecture that provides output loads access to each of the plurality of power buses. Redundant power buses are provided to each of the plurality of loads, and redundant channel controllers dictate the power bus from which each of the plurality of loads draws power, allowing a first load to draw power from a first power bus while a second load draws power from a second power bus. The present invention therefore provides the desired redundancy while utilizing the full power capacity of the two or more available power buses.

FIG. 1 is a block diagram illustrating a redundant, load-sharing system 10 according to an embodiment of the present invention. System 10 includes power buses 12 a and 12 b, protective circuits 13 a and 13 b (e.g., circuit breakers), channel controllers 14 a and 14 b, and loads 22 a, 22 b . . . 22N. Channel controller 14 a includes local power supply 15 a, microprocessor 16 a, power input terminal 17 a, input interface 18 a, power share arbitration logic 20 a, and communication output terminal 21 a. Redundant channel controller 14 b likewise includes local power supply 15 b, microprocessor 16 b, power input terminal 17 b, input interface 18 b, power share arbitration logic 20 b, and communication output terminal 21 b.

First power bus 12 a and second power bus 12 b are connected to provide power to connected loads 22 a-22N as well as operational power to channel controllers 14 a and 14 b via local power supplies 15 a and 15 b. Input interfaces 18 a and 18 b provide instructions to microprocessors 16 a and 16 b, respectively, regarding the desired operation of the loads (i.e., which loads 22 a-22N to turn On and Off, etc.). In traditional redundant power bus systems, connected loads draw power from only one of the available power buses. The remaining power bus remains un-utilized unless the primary power bus fails. This all-or-nothing approach requires protective circuits 13 a and 13 b to be sized to handle the total power requirements of all connected loads. In the present invention, the active channel controller (either channel controller 14 a or 14 b) acts to selectively allocate power from both first power bus 12 a and second power bus 12 b. Therefore, during normal operation the redundant, load-sharing system 10 is able to utilize power available on both first power bus 12 a and second power bus 12 b. In the event of a failure on one of the available power buses 12 a, 12 b, the active channel controller 14 a or 14 b re-allocates the distribution of power from the operational power bus 12 a or 12 b to the loads 22 a-22N such that the load requirements do not exceed the individual rating of the protective circuits 13 a or 13 b associated with the operational power bus 12 a or 12 b. The redundant, load-sharing system 10 therefore provides the desired redundancy while utilizing the full capacity of the available power buses 12 a, 12 b.

In the embodiment shown in FIG. 1, load control and power allocation is provided by either channel controller 14 a or channel controller 14 b, depending on which channel controller is designated as the active channel controller. For example, if both channel controllers 14 a, 14 b are operating normally, channel controller 14 a interacts with each of the connected loads 22 a-22N as the active channel controller while channel controller 14 b remains in a standby mode. In the event channel controller 14 a becomes inoperable, then channel controller 14 b is designated as the active channel controller and interacts with each of the connected loads 22 a-22N. The designated active channel control receives inputs from connected loads 22 a-22N related to the operational states of the connected loads 22 a-22N (e.g., temperature, position, etc.) and provides control instructions via communication buses 26 a and 26 b, respectively, to each of the plurality of loads 22 a-22N. While inputs from the loads are provided redundantly to both microprocessors 16 a or 16 b, only the microprocessor associated with the active channel controller will respond to the inputs received from the connected loads 22 a-22N. In this way, first and second channel controllers 14 a and 14 b are redundant to one another. If one of the channel controllers 14 a or 14 b should happen to fail, the other channel controller is available to step into the active channel controller role.

In addition to controlling the performance of each load 22 a-22N, redundant channel controllers 14 a and 14 b provide load sharing by controlling from which power bus 12 a, 12 b each connected load 22 a-22N draws power. Load sharing instructions are provided at output terminals 21 a or 21 b of the active redundant channel controller 14 a or 14 b, respectively, and communicated via communication buses 24 a and 24 b, respectively to load setting registers 25 a-25N. Each of the plurality of loads 22 a-22N are each connected to both first power bus 12 a and second power bus 12 b, and based on load sharing instructions stored by load setting registers 25 a-25N selectively draw power from either the first power bus 12 a or the second power bus 12 b. In this way, the active channel controller may direct loads to draw power from either first power bus 12 a or second power bus 12 b. For example, if first channel controller 14 a is operating as the active channel controller, first channel controller 14 a may provide load allocation instructions (via communication output terminals 21 a) instructing some of loads 22 a-22N to draw power from first power bus 12 a and some of loads 22 a-22N to draw power from second power bus 12 b, even though first channel controller 14 a is not associated with second power bus 12 b.

In the embodiment shown in FIG. 1, controllers 14 a and 14 b employ a combination of hardware and software to provide the desired load sharing. Power share arbitration logic 20 a or 20 b (depending on which channel controller is active) and software executed by microprocessor 16 a or 16 b, respectively, form a power allocation module that provides control instructions to each of the plurality of loads 22 a-22N, dictating from which of power buses 12 a, 12 b each load draws power. In other embodiments (such as that shown in FIG. 2), the power allocation module may be implemented in software stored on a computer readable medium and executed by microprocessors 16 a and 16 b. Implementing load sharing in software increases flexibility in load allocation, while implementing load sharing in hardware provides faster response times and the ability to continue load sharing operations despite faults in either of channel controllers 14 a or 14 b. It should be understood that the power allocation module and functions implemented by the power allocation module could be implemented in hardware, software executed by a microprocessor, or a combination thereof. Communication buses 24 a and 24 b (as well as communication buses 26 a, 26 b and 28) may be implemented with any well-known communication bus standard, such as the ARINC 429 aircraft communication protocol bus, Ethernet, or Controller Area Network (CAN) buses.

In the embodiment provided in FIG. 1, loads 22 a-22N may be organized into power groups. The division of loads 22 a-22N into power groups may be based on the function performed by the load, the importance of the load, and/or the power drawn by the load. For example, highly important loads may be grouped into a first power group and power allocation will always be provided to this power group before others. It may also be beneficial to group loads 22 a-22N by their expected power draws, such that the combined power drawn by a particular grouping does not exceed the individual rating protective circuits 13 a, 13 b associated with a power bus 12 a, 12 b.

The active channel controller makes a number of determinations regarding how power should be allocated from the plurality of power buses 12 a, 12 b to the connected loads 22 a-22N, based on factors such as the ratings of protective circuits 13 a and 13 b and the various nominal, transient, and worst case power profiles of the connected loads 22 a-22N. Allocating the distribution of power to ensure the individual ratings of protective circuits 13 a and 13 b are not exceeded allows the present invention to utilize the full capacity of each power bus 12 a, 12 b. For example, assume the individual rating of protective circuits 13 a and 13 b is ten amperes (10 amps) as a trip threshold, load 22 a draws four amperes, load 22 b draws eight amperes, and load 22N draws two amperes. Controller 14 a may allocate power from power bus 12 a to loads 22 a and 22N for a total of six amperes drawn from power bus 12 a, and allocate power from power bus 12 b to load 22 b, which draws eight amperes from power bus 12 b. In this way, during normal operations (i.e., both power buses 12 a, 12 b healthy) connected loads 22 a, 22 b, 22N draw a combined fourteen amperes from power buses 12 a and 12 b without exceeding the individual ratings (10 amps) of either protective circuit 13 a, 13 b.

Information regarding the nominal, transient, and worst case scenarios of each load 22 a-22N may also be incorporated into power allocation determinations. For example, in-rush currents associated with sharing a particular load (i.e., a temporary transient) may be employed by the active channel controller in allocating power to each of the plurality of loads 22 a-22N. In another example, the active channel controller may temporarily re-allocate power from a low-priority load to a high-priority load to account for high current transients drawn by the high-priority load. Decisions by the active channel controller regarding transient load requirements may be based on communications received from other controllers regarding the transient load requirements, communications received from the loads themselves (via communication from buses 26 a, 26 b), or by monitoring events on the power buses 12 a, 12 b (i.e., changes in voltage, current, etc.).

Channel controllers 14 a and 14 b further include power input terminals 17 a and 17 b, respectively, for receiving power from and monitoring the status of power buses 12 a and 12 b, respectively. In one embodiment, local power supplies 15 a and 15 b include an analog-to-digital converter (ADC) that allows microprocessors 16 a and 16 b to monitor the status (i.e., voltage, current, etc.) associated with power buses 12 a and 12 b, respectively. Alternatively, ADCs can be incorporated in the microprocessors 16 a, 16 b. Each channel controller 14 a, 14 b, even when operating in stand-by mode, monitors the status of the associated power bus 12 a, 12 b and relays this information via communication bus 28 to the opposite channel controller. In this way, the active channel controller is aware of the status of each power bus 12 a and 12 b, even those power buses 12 a, 12 b with which it is not associated.

In the event that one of the power buses 12 a, 12 b becomes unavailable, the active channel controller modifies the power allocation from a full performance mode to a reduced performance mode. This may include re-allocating power from the remaining power buses to loads previously powered by the failed power bus, reducing the power allocated to non-essential loads, or time-multiplexing the allocation of power to each of the connected loads 22 a-22N. Reducing the power allocated to non-essential loads may include removing power entirely from the non-essential loads or running the load at a reduced performance level that requires less total power. The state of each power bus 12 a, 12 b (e.g., stable, available) is monitored by the channel controller associated with the power bus. Therefore, channel controller 14 b monitors the state of power bus 12 b and communicates the status of power bus 12 b to channel controller 14 a via communication bus 28.

In addition, channel controllers 14 a and 14 b may monitor parameters such as load temperature and allocate power to the various loads 22 a-22N to compensate for the temperatures of the load and its corresponding effects on the current drawn by the load. These parameters and/or other communications provided by loads 22 a-22N are communicated via communication buses 26 a, 26 b. The state of each power bus (e.g., stable, available) is monitored by the channel controller associated with that power bus. Therefore, channel controller 14 b monitors the state of power bus 12 b and communicates the status of power bus 12 b to channel controller 14 a via communication buses 26 a and 26 b.

FIG. 2 is a block diagram illustrating a redundant, load-sharing power system 30 according to another embodiment of the present invention. System 30 includes power buses 32 a and 32 b, circuit breakers 33 a and 33 b, channel controllers 34 a and 34 b, and loads 42 a, 42 b . . . 42N. Channel controller 34 a includes local power supply 35 a, microprocessor 36 a, power input terminal 37 a, input interface 38 a, and communication output terminal 39 a. Redundant channel controller 34 b includes local power supply 35 b, microprocessor 36 b, power input terminal 37 b, input interface 38 b, and communication output terminal 39 b.

In the embodiment provided in FIG. 2, the power allocation module is implemented by software executed by microprocessor 36 a and 36 b. Each microprocessor 36 a and 36 b is connected to communicate load allocation instructions to the plurality of loads 42 a-42N via communication output terminals 39 a and 39 b. Load allocation instructions are provided via communication bus 46 a or 46 b (depending on which channel controller is active) to load setting registers 45 a-45N. Microprocessors 36 a and 36 b likewise communicate status information to one another via communication bus 48. Status information may include the status (e.g., available, health) of the power bus associated with each microprocessor. The microprocessor associated with the active channel controller executes software algorithms to make power allocation decisions based on the power capacity of available power buses 32 a, 32 b and power requirements associated with each of the plurality of loads 42 a-42N. As described with respect to FIG. 1, power allocation determinations may be based on the individual ratings of the circuit breakers as well as other nominal, transient, and worst case power profiles of the connected loads. Power allocation determinations are communicated by the microprocessor associated with the active channel controller via output terminals 39 a and 39 b. Communication buses 44 a and 44 b provide the power allocation communications to load setting registers 45 a-45N, which dictate the power bus 12 a, 12 b from which each load 22 a-22N draws power

FIG. 3 is a flowchart illustrating operations performed by either the first channel controller or the second channel controller according to an embodiment of the present invention. In this example, the embodiment shown in FIG. 1 is used, and it is assumed that first channel controller 14 a is operating as the active channel controller and second channel controller 14 b is acting as the non-active or redundant controller. Operations performed by the embodiments shown in FIG. 2 will be similar.

At step 50, first channel controller 14 a monitors the status of power bus 12 a. This may include monitoring the voltage, current or combination thereof associated with power bus 12 a to make determinations regarding the status and/or health of the power bus 12 a. For example, first channel controller 14 a may monitor the voltage provided by the power bus 12 a with respect to a threshold value to ensure the voltage provided is sufficient for supply to the attached loads 22 a-22N. In other embodiments, first channel controller 14 a determines the source (e.g., battery, generator, etc.) of power provided on the power bus 12 a based on voltage characteristics such as magnitude, frequency, etc.

At step 52, first channel controller 14 a communicates the state of power bus 12 a to second channel controller 14 b, as well as to any other redundant channel controllers. For example, as shown in FIG. 1, channel controller 14 a communicates via communication bus 28 to channel controller 14 b the state of power bus 12 a. Likewise, channel controller 14 b communicates via communication bus 28 the state of power bus 12 b to channel controller 14 a. In this way, both channel controllers 14 a, 14 b are aware of the state or condition of both power buses 12 a, 12 b.

At step 54, the active channel controller is determined. This determination may be pre-determined by hardware/software selections, or may be dynamically determined based on the status of power buses communicated between the controllers. For example, if one of the power buses 12 a, 12 b is determined to be unstable or unsatisfactory, then it may be desirable to rest control of the power allocation in the channel controller associated with the stable power bus. The non-active channel controller returns to step 50 and continues monitoring and communicating the status of the power bus with which it is associated without controlling the distribution of power to the attached loads 22 a-22N.

At step 56, the active channel controller (channel controller 14 a in this example) evaluates power demand requirements based on the loads to be operated. In the embodiment provided in FIG. 1, input interfaces 18 a and 18 b communicate instructions regarding load operation to microprocessors 16 a and 16 b, respectively. For example, the provided instructions may dictate which loads 22 a-22N are to be On and Off, the duration of operation of each load, etc. The instructions provided by input interfaces 18 a and 18 b are redundant, and although they are provided to both channel controllers 14 a, 14 b, only the channel controller associated with the active channel controller will respond to the instructions provided. The channel controller associated with the non-active channel controller may store the instructions provided, but will not respond to the instructions provided.

In addition, the instructions provided by input interfaces 18 a and 18 b will vary based on changes in operating conditions, or set-points associated with the plurality of loads 22 a-22N. The channel controller associated with the active channel is therefore continually monitoring for instructions received from input interfaces 18 a and 18 b, and in response, re-calculating the power demand requirements based on the loads to be operated.

In an embodiment related to the operation of loads on an aircraft, and more specifically to environmental control systems (ECS) employed on an aircraft, channel controllers 14 a and 14 b further receive information regarding the system state and/or flight phase. In some embodiments, depending on the system state and/or the flight phase of the aircraft, it may be desirable to reduce power to some loads to ensure adequate power is available for mission control systems during specified time periods (e.g., landing/take off). This ready redundancy ensures that if power is lost from an active channel, the backup channel is available to immediately provide power to critical loads.

At step 58, the active channel controller determines whether the power demand requirements can be satisfied by a single power bus. If the power demand requirements determined at step 56 cannot be met by a single power bus, then at step 66 the active channel controller determines whether other power buses are available to meet the determined power demand (discussed in more detail below). If the power demand requirements determined at step 56 can be met by a single power bus, then at step 60 the active channel controller determines whether it is desirable to employ more than one power bus to meet the power demand requirements of the plurality of loads 22 a-22N. Depending on the application, it may be beneficial when possible to meet the power demands of the loads 22 a-22N from a single power bus, rather than employ power from a plurality of power buses. For example, assuming channel controller 14 a is the active channel controller, and power bus 12 a is a utility power source (i.e., large capacity), power bus 12 a can be used without power contribution by power bus 12 b. In embodiments in which power bus 12 b is sourced from a battery system, it may be desirable to attempt to meet all power demand requirements from power bus 12 a, and only when the power demand cannot be met from power bus 12 a to allocate power from other channels to the loads. In another embodiment, it is desirable to allocate power to the loads from all available power buses even in the event that one power bus would be sufficient to meet the power demand requirements of the attached loads. This provides load balancing that reduces the power drawn from each individual power bus.

If it is desirable to allocate power from more than one power bus, then at step 64 the active channel controller determines whether other power buses are available (discussed in more detail below). If load allocation between more than one power bus is not desirable, then at step 62 the active channel controller allocates power from the power bus associated with the active channel controller to the plurality of loads.

If the power demand requirements can be met by a single power bus and it is desirable to do so, then at step 62 the power allocation module associated with the active channel controller allocates power from power bus 12 a to the loads. Because only a single power bus is employed, allocation of power provided at step 62 ensures that the rating of protective circuit 13 a is not exceeded. At step 64, the determined allocation of power is communicated to each of the plurality of loads 22 a-22N by power share arbitration logic 20 a. As described with respect to FIG. 1, to provide power allocation (i.e., communicate to the loads the power bus from which they should draw power), power share arbitration logic 20 a provides a communication signal to each of the respective loads 22 a-22N. In this embodiment, because of the determination that the power demand requirements of the load can be met by a single power bus, the communication provided to the respective loads instructs them to draw power from power bus 12 a. Similarly, in the embodiment shown in FIG. 2, microprocessor 36 a provides a communication signal to each of loads 42 a-42N to provide power allocation.

At step 60, if it is determined that the power demand requirements of the loads cannot be met by a single channel (e.g., power bus 12 a) or that it is desirable to allocate power to the loads from more than one power bus, then at step 66 the power allocation module of the active channel controller 14 a determines whether the power bus associated with the other channel(s) is available. Likewise, in embodiments in which it is desirable to provide load-sharing regardless of whether a single power bus is capable of meeting the power demand requirements, after evaluating the power demand requirements at step 56, the active channel controller 14 a determines whether the other channel is available at step 66.

If no other channels are available (i.e., the status of the other power buses indicates they are unavailable for supplying power to a load), then at step 68 the active channel controller allocates power to the loads from the power bus associated with the active channel controller. In instances in which the power demand requirement is greater than the power bus capability of the available power bus, then the active channel controller schedules/interleaves the operation of the loads such that the power bus capability of the power bus is not exceeded. The terms ‘schedule’ and ‘interleaved’ refer broadly to selective activation of each of the plurality of loads. That is, the loads may be turned On and Off according to a schedule that determines the state (i.e., On or Off) of each load and the duration of each cycle. Likewise, the loads may be interleaved such that each load is turned On and Off for a fixed duration of non-overlapping time. Scheduling/interleaving of the loads (i.e., selectively providing power to the attached loads) by the active channel controller may be based on factors such as priority of each load and power requirements of each load. At step 70, the channel controller communicates the instructions to the attached loads such that they draw power from the power bus associated with the active channel controller according to the communicated instruction.

If at step 66, the active channel controller determines that other power buses are available, then at step 72 the power allocation module of the active channel controller selectively allocates power from the available power buses to the plurality of loads. The allocation of power determined by the active channel controller may be based on a number of factors, including the ratings of the circuit breakers/protective circuits associated with each power bus, various nominal, transient, and worst case power profiles of the connected loads, desired performance of the loads, operating conditions of the loads, and combinations thereof. At step 74, the active channel controller communicates instructions to the loads, dictating the power bus from which each of the loads should draw power. As described with respect to FIGS. 1 and 2, the determinations of which power bus each load should draw power may be made by the channel controller associated with the active channel controller, the power share arbitration logic associated with the active channel controller, or combinations thereof.

The present invention provides a load-sharing architecture that allows redundant controllers to allocate power to a plurality of loads from all available power sources, not just the power source with which the redundant controller is associated. The present invention therefore provides the desired redundancy while utilizing the full power capacity of the two or more available power sources.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A channel controller for use in a redundant, load-sharing architecture in which each of a plurality of loads are connected to both a local power bus and a redundant power bus, the channel controller comprising: a power allocation module that monitors the status of the local power bus, receives input from a redundant channel controller regarding the status of the redundant power bus, evaluates power demands of the plurality of loads, and selectively determines an allocation of power to each of the plurality of loads from either the local power bus or the redundant power bus; and a communication output for providing power allocation instructions to each of the plurality of loads based upon the allocation of power determined by the power allocation module.
 2. The channel controller of claim 1, wherein the power allocation module determines power allocation to the plurality of loads based, in part, on expected power required by each load and power thresholds associated with the local and redundant power buses.
 3. The channel controller of claim 2, wherein the power allocation module determines power allocation to the plurality of loads based, in addition, on nominal, transient, and worst case scenarios regarding expected power requirements of each of the plurality of loads.
 4. The channel controller of claim 1, wherein the power allocation module includes a microprocessor executing software stored on a computer readable medium for making determinations regarding the allocation of power from the local power bus and the redundant power bus to the plurality of loads.
 5. The channel controller of claim 1, wherein the power allocation module includes power share arbitration logic for making determinations regarding the allocation of power from the local power bus and the redundant power bus to the plurality of loads.
 6. The channel controller of claim 1, further including: an input interface for providing instructions regarding load operation for use by the power allocation module in determining allocation of power.
 7. A method of allocating power to a plurality of loads from both a first power bus and a second power bus connected to each of the plurality of loads, the method comprising: selecting an active channel controller from a first channel controller and a second channel controller, the first chancel controller connected to receive and monitor power from the first power bus, the second channel controller connected to receive and monitor power from the second power bus; evaluating power demand requirements of the plurality of loads; allocating power to each of the plurality of loads from either the local power bus or the redundant power bus; and communicating the allocation of power from the active channel controller to the plurality of loads.
 8. The method of claim 7, wherein allocating power from the first power bus and the second power bus to the plurality of loads includes: ensuring allocation of power from the first power bus does not exceed a trip threshold of a first protective circuit associated with the first power bus; and ensuring allocation of power from the second power bus does not exceed a trip threshold of a second protective circuit associated with the second power bus. 